The present invention relates to an organic light emitting element, especially to an organic light emitting element of the type used in optical instruments having an optical device, such as a light source, for display, an optical circuit, an optical switch, an optical array, an optical communication element, a head for optical recording, and so forth.
A resonator structure formed by sandwiching an organic light emitting thin film between two plane reflectors is used in a conventional electro-luminescent element, as disclosed, for example, in a paper titled “Investigations on Multicolor Display by Organic Luminescent Devices with Optical Microcavity Structure”, by Nakayama, Tsunoda and Nagae, The Transaction of the Institute of Electronics, Information and Communication Engineers of Japan, J77-CII, pp 437443 (1994).
In an organic electro-luminescent element using a conventional micro-resonator structure, no means is provided for confining light proceeding in a direction parallel to the organic electro-luminescent film, and so light proceeding in that direction is lost. This problem occurs similarly in an ordinary type electro-luminescent element in which a micro-resonator structure is not used.
In the following, an explanation will be given as to why light proceeding in a direction parallel to an organic electro-luminescent film attenuates and is lost. At first, with reference to FIG. 11, a method of producing an organic light emitting element will be explained. Reference mark A indicates a substrate of the organic light emitting element, and a film B is formed by a vapor deposition method using an organic material. Regions to be masked from vapor deposition of the organic material vaporized in a vapor deposition source D are masked by a metal mask C.
In the vapor deposition apparatus shown in FIG. 11, a very narrow gap, which can be observed only by an optical microscope, exists between an edge of the mask C and the surface of the growing organic thin film. The gap is generated by unevenness of the substrate A, a bend in the mask C, a roundish shape of the edge part of the mask C, etc. Assuming that the width of the gap is 0.1 mm (=100 μm), and the visual angle of the vapor deposition source U viewed from the edge part is 2 deg., the variation in the growing length of the thin film is 3.5 μm (=100 pm×tan(2deg.)). That is, the thickness of the thin film changes from 100% to 0% in the interval of 3.5 μm.
Usually, since the thickness of an organic thin film, such as one used for an organic light emitting element, is about 0.1 μm, the ratio of the thickness of the organic thin film to the thickness changing interval is {fraction (1/35)}. Therefore, if the thin film is formed by a vapor deposition method using a mask, the angle of the edge part in the thin film is 1.6 deg. (=arctan({fraction (1/35)})) as shown in FIG. 12. Thus, light which enters the above-mentioned edge part of the thin film is repeatedly reflected by the inner faces of the thin film as it proceeds, as shown in FIG. 12, and attenuates until finally it is extinguished.